Hydraulic pressure master cylinder

ABSTRACT

An hydraulic pressure master cylinder has a cylinder usually of metal, and a separately made plastics reservoir. The reservoir is retained on the cylinder by means of a pair of resilient arms, the internal faces of which are recessed to conform the external surface of the cylinder. The reservoir is fitted to the cylinder by deforming the arms outwardly to enable them to shap-engage around the cylinder so that the latter seats within the recesses. If desired, the free end portions of the arms may be joined by a fixing device such as a rivet.

BACKGROUND OF THE INVENTION

This invention relates to a hydraulic pressure master cylinder for use in a hydraulic pressure system and primarily for use in the hydraulic brake or clutch actuating system or a motor vehicle. The invention is concerned with such a master cylinder of the fabricated type in which a reservoir, of moulded plastics material for example, and a cylinder of metal for example, are separately made and secured together to form a complete master cylinder.

DESCRIPTION OF THE PRIOR ART

In some conventional fabricated master cylinders, a threaded spigot projects from the underside of the reservoir and is received in a threaded hole formed in a boss projecting from the upper surface of the cylinder, in order to secure the reservoir and cylinder together. This type of arrangement necessitates expensive machining operations on at least the cylinder, and the spigot and boss connection tends to increase the overall height of the master cylinder as compared, for example, with some master cylinders in which the reservoir and cylinder are integrally formed. Since a master cylinder is usually installed in the vehicle engine compartment, often in cramped conditions, such an increase in height can be disadvantageous.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to provide a fabricated master cylinder in which the reservoir and cylinder are secured together in a simple and effective manner, which, as compared with some conventional fabricated master cylinders, leads to economy of manufacture and also to a reduction in overall height of the assembly.

According to the invention, a master cylinder comprises a cylinder and separately made reservoir mounted thereon, the reservoir and cylinder being adapted respectively to permit the passage therebetween, in use, of hydraulic fluid, the reservoir having projecting arms arranged to engage the external cylinder wall at opposite sides of the cylinder and acting to retain the reservoir and cylinder in cooperative relationship.

The cylinder-engaging faces of the arms may conveniently be shaped to follow the shape of the external cylinder wall which they engage. In one preferred arrangement, one or more pairs of arms are provided, and the arms of each pair are aligned transversely of the cylinder. The shaping of the faces may be achieved by forming recesses of appropriate shape therein and it can then be advantageous for the arms to be resilient, enabling them to be displaced outwardly by insertion of the cylinder between them until the cylinder engages within the recesses by snap-engagement.

Preferably, the arms, when transversely aligned, extend beyond the external periphery of the cylinder and are secured together by fixing means acting between their free end portions.

The reservoir is preferably formed with a projecting spigot which extends into an opening in the cylinder wall, thereby to resist displacement of the reservoir longitudinally of the cylinder. The spigot may conveniently be hollow and arranged to provide a fluid flow path between the respective interiors of the reservoir and cylinder through said cylinder wall opening.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawngs, in which:

FIG. 1 is a longitudinal cross-sectional view of one form of the master cylinder of the invention, and

FIG. 2 is an end view, partly in transverse cross-section, of the master cylinder of FIG. 1.

DETAILED DESCRIPTION

Referring to the drawings, these show a master cylinder for use in a vehicle hydraulic clutch-actuating system. The master cylinder comprises a cylinder 1 in the form of a metal tube and separately made reservoir 2, of moulded plastics material mounted thereon. The reservoir is retained on the cylinder by means of a pair of resilient arms 3, 4 which project in opposed relationship from the base 5 of the reservoir. The spacing between the opposed surfaces 6, 7 of the arms is rather less than the external diameter of the cylinder 1 and these internal surfaces are provided with respective arcuate recesses 8 having the same curvature as the external cylinder wall. The arms are sufficiently resilient to enable them to be resiliently deformed outwardly, and the reservoir is mounted on the cylinder by inserting the latter between the free end portions of the arms and applying force to urge the cylinder towards the base 5 of the reservoir until the cylinder reaches the recesses 8, whereupon the arms resiliently recover to snap-engage the cylinder into the recesses and thus retain the reservoir on the cylinder. Additional security is provided by making the arms sufficiently long to project beyond the periphery of the cylinder and securing the projecting end portions together by the passage therethrough of a fixing device shown as a rivet 9. The fixing device may also act to squeeze the arms together and so increase the retention force.

The base 5 of the reservoir has a downwardly projecting flange 10 defining a chamber 11 in the general form of a rectangle of which the short sides, disposed longitudinally of the cylinder are outwardly curved. A hollow spigot 12 extends from the interior of the reservoir into the chamber 11 and extends beyond the outer extremity of the flange 10 by a distance which is slightly less than the thickness of the cylinder wall. The diameter of the spigot 12 is such that it fits closely within an opening 13 through the cylinder wall and acts to resist displacement of the reservoir longitudinally of the cylinder. The degree of extension referred to above of the spigot beyond the flange 10 ensures that the spigot does not form an obstruction within the cylinder. The spigot 12 and opening 13 also provide a first fluid path between the reservoir and cylinder. A transverse passage 14 in the spigot provides a communication between the reservoir and chamber 11 and a second fluid path is established between the reservoir and cylinder through the chamber 11 via an opening 15 in the cylinder wall portion underlying the chamber. A resilient sealing ring 16 conforms to the peripheral shape of the chamber 11 and provides a fluid-tight seal between the chamber and the external wall of the cylinder.

A piston assembly, generally designated 17, is slidably reciprocable within the cylinder 1 under the control of a driver-operated clutch pedal (not shown) connected to the piston assembly by means of a rod 18 provided with a part-spherical end 19 which is housed within a correspondingly shaped recess in the piston assembly and retained by a keeper 20.

A radial flange 21 at the forward end of the piston assembly supports a primary seal 22 mounted on a nose 23 of the assembly and held in place by a retainer 24. A secondary or back-up seal 25 is supported by a rear end portion 26 of the piston assembly and located by a radial flange 27.

The cylinder 1 is formed with its forward end portion 28 tapered inwardly and its rear end portion 29 flared outwardly. The forward end of the cylinder is closed by a plug 30, which either is resilient enough to conform to the internal taper of the cylinder end portion 28, or of which the outer surface is already tapered to match the cylinder taper. The plug 30 is passed along the cylinder from the flared end portion 29 into the tapered forward end portion prior to insertion of the piston assembly 17, and a retainer 31 is subsequently placed in a groove in a projecting end portion of the plug to prevent it from being pushed back into the cylinder. A seal 32 prevents leakage of fluid past the plug. A pipe 33, for connecting the master cylinder to a slave cylinder for example, is expanded into the plug and is afforded support by a hollow insert 34.

In order to close the rear end of the cylinder a collar 35, the internal surface of which is preferably tapered to be complementary to the cylinder end portion 29, is engaged over the inwardly tapered cylinder end portion and, before mounting of the reservoir, is passed along the cylinder onto the outwardly tapered portion 29 until a radial flange 36 of the collar is flush with the rear end of the cylinder. After the piston assembly 17 has been installed in the cylinder, an annular plate 37 and a closure boot 38 are passed along the rod 18, the plate 37 being engaged within a groove 39 of the boot and secured to the flange 36 by any appropriate means such as riveting or bonding for example the boot being thus retained in position by the plate 37. The latter projects radially inwardly beyond the inner surface of the cylinder end portion 29 and forms an end stop 40 to retain the piston assembly 17 within the cylinder.

The piston assembly 17 is shown in its rearmost position, as determined by the end stop 40, in which the reservoir is in communication via the hollow spigot 12 with the chamber 41 behind the flange 21 of the piston assembly and via the spigot 12, chamber 11 and opening 15 with the chamber 42 in front of the flange 21, so that both chambers are full of fluid. In order to actuate a device such as a clutch slave cylinder connected to the pipe 33 the piston assembly is advanced along the cylinder by operation of the clutch pedal and, after a short travel of the assembly, the flange 21 covers the opening 15, following which, further advancement of the piston assembly causes a build-up of pressure in the chamber 42 which is transmitted via the pipe 33 to actuate the slave cylinder. As the piston assembly advances, fluid passes from the reservoir via the hollow spigot to fill the chamber 41 as it increases in volume. Retraction of the piston assembly displaces fluid via passages 43 in the flange 21 and past the seal 22 from the chamber 41 to the chamber 42.

The master cylinder of the invention may take various alternative forms. For example, the arms may be disposed in staggered relationship along the reservoir instead of aligned in the manner described. More than one pair of arms may be provided along the body of the reservoir. The arms may be arranged to extend laterally either from the side or base of the reservoir, rather than longitudinally from the base as illustrated. Instead of being recessed as described, the arms may be simply curved to fit around the cylinder. The retention force may be provided substantially entirely by the fixing means acting at the free end portions of the arms, rather than by the inherent resilience of the arms.

It will be seen that, by virtue of the invention, the base 5 of the reservoir is brought into close proximity with the peripheral surface of the cylinder and this enables the overall height of the assembly to be minimised. Moreover, because the reservoir fits directly over the external surface of the cylinder, communication between the reservoir and cylinder interiors may be readily achieved by forming appropriate holes through the cylinder wall, which may be effected by a simple drilling operation. Since the reservoir may conveniently be made by moulding from plastics material, and requires little or no machine finishing, it will be seen that machining of the major components is minimised. 

I claim:
 1. In a hydraulic master cylinder assembly comprising a cylinder having a bore therethrough, a piston operably disposed within said bore for reciprocating movement therein, at least one opening through the peripheral wall of said cylinder, a separate hydraulic fluid reservoir member removably mounted on said cylinder, a spigot on said reservoir projecting therefrom and extending into said opening so as to resist longitudinal displacement of said reservoir with respect to said cylinder, and a bore through said spigot providing a fluid flow path between the respective interiors of said reservoir and cylinder, the improvement comprising mounting and retaining arms on said reservoir and projecting therefrom to engage the peripheral outer wall of said cylinder on opposite sides thereof comprising at least one pair of spaced parallel resilient arms attached to and extending from said reservoir at least substantially beyond the central axis of said master cylinder, cylinder engaging recesses on the inner surfaces of said arms shaped to conform to the outer peripheral surface of the cylinder and extending from a position between the reservoir and the axis to a position beyond said axis to engage said peripheral surface for a distance on the side opposite said reservoir so that said arms are resiliently displaceable outwardly for insertion of the cylinder between them until the cylinder engages with the recesses by snap-engagement to securely retain said reservoir on said cylinder by the gripping force produced by the resiliency of said arms.
 2. A master cylinder assembly according to claim 1, whereinsaid mounting and retaining arms comprise a plurality of pairs of arms wherein the arms of each pair are aligned transversely of the cylinder.
 3. A master cylinder assembly according to claim 2, wherein each pair of arms extends beyond the external periphery of the cylinder on the side opposite said reservoir, and further comprising a fixing means attached to the free end portions of each pair to secure them together. 